Plant Care: Fertilize Plants Properly

We feed our fish carefully and take care of their well-being. But our plants also need sufficient nutrition and suitable water values if a beautiful aquarium is to be created.

Water Values

Most plants prefer soft, slightly acidic water, but they can also tolerate normal tap water well. This is why the water values ​​are of minor importance for most of the plants that can be bought in stores. They adapt to the circumstances – provided the diet is right.

The Liebig Principle

The Liebig or minimum principle applies to all plants and, of course, to those in the aquarium, made famous by the famous German chemist Justus von Liebig in the 19th century, especially in agriculture. After that, the growth of the plants is restricted by the least amount of nutrients available. This means that all nutrients must be available in sufficient quantities for the plants to grow optimally.

Macro and Micronutrients

Some nutrients are little used, others a lot. While the micronutrients (often also referred to as trace elements) can often be added in sufficient quantities through regular water changes, but in any case with a universal fertilizer from specialist shops, this is different with macronutrients.

The Main Macronutrients

Macronutrients mean that there must be a relatively large amount of them. The most important macronutrients are now presented.


Good lighting is essential. Modern LED lights with full-spectrum or RGB are ideal prerequisites for providing this nutrient in sufficient quantities. The amount of light required also depends on the plants. Rosette plants such as spear leaves (Anubias), water goblets (Cryptocoryne), Java fern (Microsorum pteropus), or many mosses need little light, about 0.1 watts per liter are sufficient, depending on the height of the aquarium. Plants with higher demands such as Amazon sword plants (Echinodorus) or most stem plants get along better with 0.2 to 0.3 watts per liter.

Carbon Dioxide

Carbon dioxide (CO2) is a gas that normal air already contains about 0.04%. It also dissolves in aquarium water, but in a small amount. Fish and other aquarium inhabitants produce CO2. Usually, however, this is far too little for the plants. That is why many aquarists use all kinds of CO2 systems, from simple to very complex. However, only the free CO2 can be absorbed by the plants. And that is only available in sufficient quantities if the water is relatively soft (below 4 ° KH, carbonate hardness) with a pH value just below 7. Only then can very good plant growth be expected.


The first fertilizers offered for the aquarium were iron fertilizers. That shows the importance. If there is a lack of iron, growth stops and young leaves turn yellow. Iron (Fe2 +) can be added in two ways. On the one hand, when setting up the aquarium, a special nutrient medium can be introduced as the bottom layer, which e.g. contains laterite or clay as a source of iron. There are also special long-term fertilizers for the substrate, which also contain a lot of iron. This is used for the root supply. But since the plants also absorb their nutrients through the leaves, adding fertilizer with iron, as in all complete fertilizers, makes sense.


Nitrogen is mostly absorbed as nitrate (NO3-). The nitrate is regularly supplied through the waste from the aquarium inhabitants, leftover food, and decomposing plant parts. There is usually enough nitrate in tap water too, which is added when the water is changed. Only in sparsely populated aquariums with many plants can nitrate become a deficiency. Special fertilizers are offered for this, which should only be used then.


Phosphorus is available as phosphate – usually in completely sufficient quantities. Too much phosphate leads to strong algae growth. That is why phosphate practically never has to be added. Tip: You should inquire at the local waterworks whether phosphate is added to the tap water (a permitted method for pipe protection). Then a phosphate binder from specialist retailers makes sense to keep algae growth in check.


A widely underestimated plant nutrient is potassium (K +). It is usually only contained in tap water in small quantities and should be added. Good complete fertilizers contain sufficient proportions of it.

More Nutrients for Plants

The other nutrients such as calcium, magnesium, sulfur, copper, boron, manganese, zinc, molybdenum, nickel, and cobalt are only required in small quantities, so they are micronutrients. Calcium and magnesium, like sulfur (as sulfate), are available in sufficient quantities in tap water and are added when the water is changed regularly. The other nutrients are contained in every good complete fertilizer, which is why using them in the intended concentration in addition to the other nutrients mentioned here ensures that the plants in the aquarium grow optimally.

Mary Allen

Written by Mary Allen

Hello, I'm Mary! I've cared for many pet species including dogs, cats, guinea pigs, fish, and bearded dragons. I also have ten pets of my own currently. I've written many topics in this space including how-tos, informational articles, care guides, breed guides, and more.

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